CAREER: Stratified Mixing in Sheared and Zero-Mean-Shear Turbulent Environments

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Mechanisms by which mass transport and mixing occur remain to be well-understood in flows for which there are interacting sources of energetic turbulence. The primary aim of this project is to evaluate various types of mass transport that occur from the interaction between mean shear stress (i.e. generated by velocity gradients in unidirectional flow) and instantaneous and localized shear stress generated by chaotic turbulence in the presence of density stratification. Findings from this work will improve understanding of deep ocean mixing, brine discharges in bays or subglacial lakes, saltwater intrusions in rivers, and avalanches, among others. The work will include mentorship of a graduate student and undergraduate researchers through the Graduates Linked with Undergraduates in Engineering program that supports women in STEM. The PI will develop large-scale public engagement events surrounding environmental mixing processes through art exhibits and educational modules. Further, the research team will partner with a local science museum to develop a permanent exhibit as well as a hands-on laboratory workshop for K-12 home-schooled students to study gravity currents; data generated from these experiments will be shared with the research community. The overarching goal of this research is to comprehensively evaluate the independent and combined roles of energetic turbulent flows with and without current-generated shear acting upon density-stratified fluid systems. This will be achieved via a comprehensive laboratory approach using unique and highly controllable facilities that allow full quantification of links between flow energetics, buoyancy, and fluid properties with mixing and mass transport dynamics. Three distinct flow scenarios will be considered: turbulence with no mean current, a density current released into fluid with background turbulence, and advection of turbulence over a density interface. Non-invasive quantitative imaging techniques will be used to measure velocity and mass concentration fields to characterize flow dynamics. This systematic approach will provide an understanding of how competing sources of turbulence contribute to mixing and transport, particularly when shear-driven flows act in conjunction with background turbulence. Impacts are expected to be far-reaching, with direct and practical means for implementing the scientific knowledge gained through the laboratory and synthesis efforts. Additionally, significant outcomes are expected via the complementary educational and public outreach activities designed to engage women and home-schooled K-12 students, along with the general public. These activities will be assessed annually throughout the duration of the proposal period to foster continued improvement of equity, diversity, and inclusivity in STEM.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.